A structure of a carbon nanotube (hereinafter, referred to as CNT) was first found in 1991. Synthesis, physical property, and application of the carbon nanotube have been actively studied. Also, it has been confirmed that the CNT is produced by adding transition metals, such as ferrum (Fe), nickel (Ni), cobalt (Co), etc., at the time of discharging electricity. A full study started from a preparation of a significant amount of samples by a laser evaporation method in 1996. The CNT takes a form of a round wound hollow tube whose graphite surface is a diameter of a nano size. At this time, the CNT has electrical characteristics, such as conductor, semiconductor, etc., according to the wound angle and structure of the graphite surface. Moreover, the CNT is divided into a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT), a thin multi-walled carbon nanotube, a multi-walled carbon nanotube (MWCNT), and a roped carbon nanotube according to the number of graphite walls.
In particular, the CNT has excellent mechanical strength or elastic strength, chemical stability, eco-friendliness, and electrical conductor and semiconductor property as well as has an aspect ratio larger than the existing any materials, wherein the aspect ratio reaches about 1,000 as a diameter of 1 nm to several tens nm and a length of several μm to several tens μm. Also, the CNT has a very large specific-surface area. As a result, the CNT is being interested as advanced new materials, which will lead the twenty-first century, in the field of next-generation information electronic materials, high-efficiency energy materials, high-functional complex materials, eco-friendly materials, and the like.
However, in spite of various advantages owned by the CNT, since the CNT has very large agglomeration phenomenon and very large hydrophobic property, the CNT is very poor in terms of the mixed property with other media as well as does not have solubility to organic solvents in addition to water Therefore, in order to expand the applications of the CNT while having the advantages of the CNT, a method capable of increasing compatibility with various media and making dispersion efficiency good is needed As a technology of increasing the compatibility of CNT, there is a functional group substituting technology capable of providing separate characteristics on a surface, for example, there are a method for increasing the specific-surface area of CNT using strong bases such as potassium hydroxide, sodium hydroxide, etc., under vacuum and inert gas atmosphere as described in KR Patent No. 450,029, a method for functionalizing a CNT using strong acids or strong bases as described in KR Patent Publication Nos. 2001-102598, 2005-9711, and 2007-114553, and a method of providing a functional group through a process of several steps using organic/inorganic compounds simultaneously with using strong acids or strong bases as described in Chem. Rev, 2006, 106, 1105-1136 as a reference document.
However, since the above technologies use strong acids, such as nitric acid, sulfuric acid, etc., or strong bases, such as potassium hydroxide, sodium hydroxide, etc., they are harmful to environment, are not easy to handle, and can cause the corrosion of a reactor. Further, since the above technologies use organic/inorganic materials, a large amount of harmful wastes can occur. In addition, since they have long reaction time and limited throughput such as subjecting to several reaction steps, the efficiency is low and in order to provide the functional group in addition to oxygen on the surface, they need separate processes, such that much cost and time are consumed.